I added 2 sub domains and I only want them to have access
to their own sub domain. There’s jeff.despiseme.com anddmofia.despiseme.com. When I login with MY FTP program, I
can access their all folders. How do I only allow them to see
their own seperate folder?

You would need to add a new user to your account. Each user can have his own home directory, and it is this home directory which is used as the root for FTP access. After you create the user you should then be able to edit the subdomains to have them included in the user’s directory.